| Budget Amount *help |
¥3,710,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥210,000)
Fiscal Year 2007: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2006: ¥2,800,000 (Direct Cost: ¥2,800,000)
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| Research Abstract |
The d-wave order parameter of heavy-fermion superconductors have been investigated for CeCu_2Si_2, CeCoIn_5, CeIrIn5 using Josephson effect and point-contact spectroscopy. The Josephson junctions between these materials and Al were fabricated and the magnetic field dependence of Josephson critical current was measured. For CeIrIn5, Fraunhofer diffraction patterns have been observed for the [100], [110] and [001] directions, possibly suggesting conventional BCS-like superconductivity. In contrast, CeCoIn5 has shown an oscillating pattern for the junction along the [001] direction, which does not contradict with the dx_2-y_2 state. Polycrystalline CeCu_2Si_2 also showed a diffraction pattern in spite of several tens of crystallites included in the junction area. This result cannot be understood in terms of d-wave superconductivity, if the directions of the crystallites are at random. For point-contact spectroscopy, a Pt-needle was gently pressed onto the sample with a commercial piezo-electric actuator. Some of the contacts on CeCoIn_5 have shown spectra that are typical of tunneling effect. The energy gaps Δ derived from the spectra are within the scattering range of the reported values, and the temperature dependence of Δ differs from that of conventional BCS superconductors. CeIrIn5, on the other hand, only gave the spectra that reflect the superconducting transition of the bulk resistance, so that a precise value of the energy gap cannot be determined.
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